Reciprocating internal combustion (IC) engines are known for converting chemical energy from a fuel supply into mechanical power. An air/fuel mixture is received in a variable volume of an engine cylinder, where it is compressed and burned. The burning mixture expands, thus providing mechanical work. The mechanical work produced by one or more engine cylinders is collected by various mechanisms and used to rotate a shaft, which provides useful engine work.
The expanding air/fuel mixture becomes exhaust gas after the burn has completed, which exhaust gas can include various chemical constituents including nitrogen oxides (NOx), unburned hydrocarbons (UHCs), and particulate matter (PM). The amount or concentration of such and other constituents that are produced as a byproduct of engine operation may be subject to government regulation.
One type of engine operation that has been known to yield reduced amounts of undesired exhaust constituents is HCCI, which is known to produce a more complete burn that traditional engines, and at a relatively lower temperature. While the various characteristics of HCCI combustion are preferred for the reduced emissions that are produced, HCCI combustion is typically difficult to control in a real-world application where temperature variations and transient engine operating conditions are the norm.